Whosoever's sins you remit, they are remitted unto them; and whosoever's sins you retain, they are retained.
All Commentaries on John 20:23 Go To John 20
George Leo Haydock
AD 1849
Whose sins you shall forgive These words clearly express the power of forgiving sins, which, as God, he gave to his apostles, and to their successors, bishops and priests, to forgive sins in his name, as his ministers, and instruments, even though they are sinners themselves. For in this, they act not by their own power, nor in their own name, but in the name of God, who as the principal cause, always remitteth sins. This is generally allowed to be done by God's ministers in the sacrament of baptism, as to the remission of original sin; and the Catholic Church has always held the same of God's ministers, in the sacrament of penance. (See the Protestant Common Prayer Book, in the Visitation of the Sick.)
Whose sins you shall retain, they are retained: by which we see, that to priests is given a power to be exercised, not only by forgiving, but also by retaining; not only by absolving and loosing, but also by binding, by refusing, or deferring absolution, according to the dispositions that are found in sinners, when they accuse themselves of their sins. From hence must needs follow an obligation on the sinner's part, to declare, and confess their sins in particular, to the ministers of God, who are appointed the spiritual judges, and physicians of their souls. A judge must know the cause, and a physician the distemper: the one to pronounce a just sentence, the other to prescribe suitable remedies. (Witham)
See here the commission, stamped by the broad seal of heaven, by virtue of which, the pastors of Christ's Church absolve repenting sinners upon their confession. (Challoner)